| 微观结构对镍基高温合金腐蚀行为影响的研究 | |
| Alternative Title | The Influence of Micro-structure on a Ni-based Super alloy’s Corrosion Behaviors |
| 刘莉 | |
| Subtype | 博士 |
| Thesis Advisor | 王福会 |
| 2007-10-09 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 金属研究所 |
| Degree Discipline | 材料学 |
| Keyword | 腐蚀 Ni基高温合金 单晶合金 纳米化 |
| Abstract | 本文根据镍基高温合金在不同使役环境中可能遭受的各种腐蚀形式，选择常温电化学腐蚀、盐和水蒸气协同作用下的中温腐蚀以及高温氧化三种腐蚀环境，针对三种微观结构（单晶、多晶及纳米晶）的镍基高温合金的常温电化学腐蚀和高温腐蚀行为进行了详细研究，为研究上述三种微观结构材料在盐和水蒸气协同作用下的中温腐蚀，同时对相应的电化学测试技术进行了初步探索。本文较为全面地阐明了三种材料在各腐蚀环境中的腐蚀行为，为进一步改善镍基合金的抗腐蚀性能提供了必要的理论依据。 在常温电化学腐蚀方面，对三种材料在酸性不含有氯离子溶液中的研究结果表明，三种不同微观结构的镍基高温合金（单晶、多晶及纳米晶）具有相近的腐蚀行为；当溶液中含有侵蚀性氯离子时，三种材料呈现出不同的腐蚀行为。氯离子在纳米晶表面的吸附量显著小于其在单晶和多晶表面的吸附量，大量吸附的氯离子参与了单晶和多晶表面钝化膜的形成，并导致了其钝化膜半导体类型的转变，由原有的p型转变成n型。半导体类型的转变和氯离子的掺杂降低了单晶和多晶合金的抗腐蚀能力，生成具有不含氯离子的p型半导体膜的纳米晶涂层则具有更强的抗腐蚀能力。在酸性体系中，纳米化提高镍基高温合金的抗Cl离子腐蚀能力。 在酸性含氯离子体系中，研究发现溅射纳米晶涂层的抗腐蚀能力随晶粒尺寸减小而提高。对三种不同晶粒尺寸的纳米晶涂层钝化膜内载流子的扩散系数进行理论计算，从理论上说明了三种纳米晶涂层的抗腐蚀能力的大小。实验结果表明晶粒尺寸的减小会降低氯离子表面吸附量、利于元素扩散促进致密钝化膜的形成及提高钝化膜的自修复能力。因此，随材料晶粒尺寸的减小，材料的抗腐蚀能力提高。 三种材料在3.5%NaCl溶液中表面生成的钝化膜的成分和致密性严重影响了材料的抗腐蚀能力。多晶合金表面生成的含有较多NiO，并且致密性最差的钝化膜的抗腐蚀能力在三种材料中最差。单晶合金表面形成的含有较少NiO，致密性较好的钝化膜对Cl离子有一定的阻挡作用，因此其抗腐蚀能力其次。纳米晶涂层表面形成的不含NiO，致密性最好的钝化膜有效抵御Cl离子的侵蚀，其抗腐蚀能力最强。材料的微观结构影响了表面钝化膜生成机制，导致形成不同成分的钝化膜，而且对钝化膜后期生长过程也有影响，导致生成钝化膜的致密性的严重差别。这些因素严重影响了材料的腐蚀行为。 在盐和水蒸气协同作用下的中温腐蚀中，首先利用测量电偶电流的方法证明在盐和水蒸气协同作用中存在电化学反应，从而在实验上证实了前人提出的观点。而后探索了适当的电化学测试方法。交流阻抗测量结果显示阻抗谱只存在一个反映氧化物层的低频容抗弧，测量所得的电阻和电容值会随着反应时间和反应气氛的变化而变化，其中氧化物电阻能够反映腐蚀速度，氧化物电容能够反映腐蚀过程，进而证明交流阻抗技术可以在该领域应用。该部分实验结果不仅证实在中等温度NaCl和水蒸气协同作用下存在电化学反应，也探索出一种可以测量这种电化学反应的有效方法，为以后的研究工作提供前提条件。 在高温氧化研究方面，三种材料在1000℃恒温氧化研究结果显示，多晶合金抗氧化能力最差，单晶其次，纳米晶最好。单晶合金形成较均匀的氧化层，并且最内层最终形成连续的Al2O3层，对合金的氧化起到了有效的保护作用。多晶合金表面形成不均匀氧化物，并且发生严重内氧化，导致氧化增重随时间增加而不断增加，抗氧化能力降低。纳米晶涂层提供大量的扩散通道，有效降低Al2O3的形成临界含量，使表面初期就形成连续的Al2O3层，有效提高合金的抗氧化能力。循环氧化结果表明，循环氧化后，单晶合金氧化物脱落，但有连续Al2O3层生成，有一定的抗循环氧化能力。不均匀氧化降低多晶合金的抗循环氧化能力。纳米晶涂层表面Al2O3层具有较好的黏附性，因此其抗循环氧化能力也很强。在水蒸气中，单晶合金表面生成大量Cr2O3，H2O与其生成大量挥发性物质。多晶合金表面形成大量TiO2，其抑制Cr2O3挥发。纳米晶涂层表面生成Al2O3连续层，随水蒸气含量的提高，连续层生成的时间延长。微观结构影响了三种微观结构材料生成氧化膜的机制、厚度、形态，导致其氧化和腐蚀行为的显著差异。 |
| Other Abstract | The corrosion behaviors of a Ni-based superalloy with polycrystalline, single-crystalline (SC) and nanocrystalline (NC) have been studied in aqueous solution at normal temperature and at high temperature. In order to study the corrosion behavior of three materials under the synergistic effect of NaCl and water vapor at middle temperature, some effective electrochemical techniques had been explored with pure metals as specimens. The influence of microstructure on the corrosion behavior of Ni-based superalloy had been studied in details under different corrosive environments. These results are very useful for people to understand the corrosion mechanism of Ni-based superalloy and afford the theoretical base to improve the corrosion resistant of this alloy in future. The electrochemical corrosion behavior of a Ni-based superalloy with polycrystalline, single-crystalline (SC) and nanocrystalline (NC) have been studied in 0.25M Na2SO4 + 0.05 M H2SO4 and 0.5 M NaCl + 0.05 M H2SO4 solution respectively. The corrosion behaviors of three materials were semblable in Na2SO4 acidic solution, while the NC coating had superior resistance to pitting corrosion among three materials in NaCl acidic solution. The corrosion behaviors of the cast alloy and the SC alloy were similar in NaCl acidic solution. The semiconductive type of passive film of the NC coating was p-type in both acidic solutions, while, that of cast alloy and SC alloy changed from p-type in Na2SO4 acidic solution to n-type in NaCl acidic solution. XPS results indicated that no chloride ion was found in the passive film of NC coating while it was in the passive films of cast alloy and the SC alloy. The chloride ions adsorbing on the surface of cast alloy and SC alloy incorporated into the passive film, which induced the formation of n-type oxide film. The nanocrystallization of Ni-based superalloy obviously weakened the adsorption of chloride ions on surface, which decreased the susceptibility of pitting corrosion in acidic solution. The electrochemical corrosion behavior of three Ni-based superalloy nanocrystalline(NC) coatings with the same composition and different grain size, fabricated by a magnetron sputtering technique, has been investigated in 0.5 M NaCl + 0.05 M H2SO4 solution. The NC coating with 100 nm grain size formed a porous passive film in NaCl acidic solution which permitted the chloride ions to penetrate the film, and thus increased the susceptibility to pitting corrosion. The NC coating with 10 nm and 50nm grain size formed a compact non-porous passive film in NaCl acidic solution which increased the resistance to pitting corrosion. The small gain size produced by the nanocrystallization had three beneficial effects: it gave a uniform elemental distribution, which decreased the amount of chloride ions adsorbed on the surface, it promoted the formation of compact passive film and it increased the repassivation ability of the superalloy. All of the effect of small grain size greatly increased material’s resistance to pitting corrosion in acidic solution. The electrochemical corrosion behavior of three materials has been studied in 3.5% NaCl solution. The results indicated that among three materials, the corrosion resistance of the NC coating was the highest, that of the SC (200) alloy was in the next place and that of the cast alloy was the lowest. XPS results showed the composition of passive film on three materials was different. Except Cr2O3 and TiO2, there were a little of NiO in the passive film on the cast alloy, little in that of the SC (200) alloy and none in that of the NC coating. The double-log plots showed the compact property of the passive film formed on the cast alloy was the worst, that on the SC (200) alloy was the second one and that on the NC coating finally was the best one among three materials. The micro-structure influences both of the composition of passive film and the initial growth of passive film. Those determined the compact property of the film and lead to the difference of the corrosion behaviors of three materials. The corrosion behavior of pure Fe and pure Cr at 600℃ under a deposit of solid NaCl was accelerated by the involvement of water vapor into the system. The corrosion current was tested, which testified the existence of electrochemical reactions during the whole reaction. In EIS measurement, only one capacitive loop obtained on the pure Fe and Cr coated with solid NaCl and gave the information of oxide layer on them. For the oxide in air, there is a good relationship between the Rox and the reaction rate for both pure Fe and Cr with different oxide time. The lower the Rox is, the higher the reaction rate is. Although no good relationship can be set up between the Rox and the reaction rate when water vapor presented, its trend with oxide time for both metals is generally in accordance with that of the corrosion rate measured by the mass gain curves. The electrochemical technique is an effective method for studying corrosion performance at high temperature. The oxidation behavior of three materials was studied at 1000℃. The isothermal oxidation results indicated that the oxidation rate of nanorystalline coating was the lowest among three materials. At the initial stage, the oxidation rate of single-crystal alloy was faster than that of cast alloy, while at later stage, it was slower than that of cast alloy. A non-uniform external oxide of which some locations were nodule-like scale was formed on surface of cast alloy after oxidation 50 hours at 1000℃. The nodule-like parts consisted of TiO2, Cr2O3 and serious internal oxidation of Al, and rest flat surface was an Al2O3 layer. The non-uniform oxide layer and internal oxidation which produced by defects and large scale grain boundaries on the cast alloy, which decreased the oxidation resistance. For single-crystal alloy (200), uniform oxides scale consisted of external Cr2O3 with little TiO2 and internal continuous Al2O3, which lead to good oxidation resistance. For sputtered nanocrystalline coating, a continuous Al2O3 layer formed, which increased the material’s oxidation resistance. The cyclic oxidation results indicated that oxidation layer on the SC alloy scaled off, but a continuous Al2O3 layer formed at later stage, therefore the mass gain had a stable value. A non-uniform external oxide and internal oxidation decreased the resistance to cyclic oxidation of the cast alloy. The continuous Al2O3 scale has good adhesion, which increased the resistance to cyclic oxidation of the NC coating. The experiments in H2O indicated that the difference of microstructure influence the effect of H2O to materials. H2O reacted with Cr2O3 on the SC alloy to form volatile products because there were a lot of Cr2O3 and little TiO2 formed on it. A large amount of TiO2 formed on the surface of the cast alloy, which inhibited the reaction of Cr2O3 with H2O. H2O prolonged the time to form a continue Al2O3 layer on the NC coating. The crystal structure influenced the oxidation and corrosion mechanism and resulted in different oxide scale for the three materials. |
| Pages | 107 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/17026 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 刘莉. 微观结构对镍基高温合金腐蚀行为影响的研究[D]. 金属研究所. 中国科学院金属研究所,2007. |
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